Osteomalecia is a serious impediment to rehabilitation of patients with chronic renal failure treated by dialysis. Studies in the past two years in our laboratory have demonstrated sialoprotein-chondroitin sulfate antigens that appear to be specific for mineralizing cartilage and bone. The distribution of these antigenic materials in skeletal tissues parallels the distribution of noncrystalline calcium in the tissues. Calcium in this form appears prior to deposition of crystalline calcium phosphate, initially only in cartilage adjacent to mineralized bone. We propose to continue work on the isolation and biochemical characterization of these antigens and to continue efforts to obtain monospecific antisera against them. Monospecific antisera will be used to study the localization of the antigens in tissues and cells of developing chick embryo bones and cartilage and in tissue cultures of chick embryo osteoblasts and chondrocytes. Localization of antigens will be correlated with the localization of calcium and phosphate as demonstrated by histochemical and radioautographic techniques in the same tissues and cells. These studies will provide basic new data about the role of sialoprotein-chondroitin sulfate complexes in mineralization of skeletal tissues which will ultimately result in improved therapy of patients with metabolic bone diseases.